Background - Ad hoc networks contain laptop
computers, Personal Data Assistants (PDAs), embedded sensors or other wireless
devices that self-organize into a multi-hop communications network. Devices are
typically mobile and may enter or leave the network at any time. Ad hoc
routing extends communication beyond the radio signal range by relaying data
packets through intervening devices, enabling packets to "hop" across devices to
the final destination. Because ad hoc networks do not depend upon a fixed
infrastructure, they are ideal for disaster scenarios where cables and routers
have been damaged, or for remote areas where no infrastructure exists. In
addition to disaster response and military operations, ad hoc networks are being
developed for applications as diverse as inter-vehicular communication, space
networks, and environmental monitoring. Devices and applications vary greatly in
communication patterns, mobility, and operational constraints such as battery
size. No single routing algorithm is well suited to all situations. However,
current designs build the ad hoc protocol into the operating system or custom
hardware, thereby forcing all applications to use the same routing algorithm and
adding complexity to protocol development and modification.

Approach - Our program offers two important
advancements for ad hoc networks:

A design and prototype software that support
multiple ad hoc routing protocols on each device, and that allow applications
to select the most suitable protocol.

Use of off-the-shelf laptop computers and PDAs
without special hardware or modifications to the operating system.

We achieve these goals by building an ad hoc routing
(AHR) network layer on top of the IP network layer. The AHR layer replaces the
IP interface to applications, and provides both packet forwarding and route
discovery services. Each ad hoc routing protocol that plugs into our framework
supplies its own algorithm for discovering routes and for maintaining the
routing lookup tables. Our AHR framework deploys multiple ad hoc servers that
run different plug-in protocols. An application selects its routing protocol by
selecting the associated AHR server.

Accomplishments - An operational prototype of
the AHR software layer has been developed and is installed on a heterogeneous
testbed of six devices. The testbed consists of a Windows 2000® laptop computer, a
Windows XP® laptop computer, and four Compaq iPAQ PDAs, each equipped with an IEEE
802.11b "Wi-Fi" network card in ad hoc mode (no access point is used). To
demonstrate AHR operations, we developed interactive visualization software
that, in real-time, probes the network, shows which devices are reachable from
the visualization host, and displays the path between any source-destination
pair.